Detect and Fit Circle

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Description

This Step is used to fit a circle to the circular edge detected from the image.

Usage Scenario

This Step is mainly used for automatic inspection, center localization, radius measurement of workpieces or parts with circular contours.

Basic Concepts

Caliper

In image processing, a virtual measurement tool detects edges within a specified region. Adjusting its count, width, and length affects the accuracy and stability of edge detection.
Edge polarity

It refers to the direction of grayscale change across an edge, e.g., dark-to-light or light-to-dark.

Input and Output

Input

Input port	Data type	Description
Image	Image	The image used for detecting a circular edge.
Alignment Parameter Group	Pose2D	Used to adjust the target region’s pose in sync with the target object’s pose changes.

Input port

Data type

Description

Image

The image used for detecting a circular edge.

Alignment Parameter Group

Pose2D

Used to adjust the target region’s pose in sync with the target object’s pose changes.

Output

Output port	Data type	Description
Fitted Circle	Shape2D/Circle	The circle obtained through fitting.
Circle Center	Shape2D/Point	The center of the fitted circle.
Circle Center X	Number	The X coordinate of the center of the fitted circle.
Circle Center Y	Number	The Y coordinate of the center of the fitted circle.
Radius	Number	The radius of the fitted circle.

Output port

Data type

Description

Fitted Circle

Shape2D/Circle

The circle obtained through fitting.

Circle Center

Shape2D/Point

The center of the fitted circle.

Circle Center X

Number

The X coordinate of the center of the fitted circle.

Circle Center Y

Number

The Y coordinate of the center of the fitted circle.

Radius

Number

The radius of the fitted circle.

Parameter Description

Parameter	Description
ROI Settings	A circular ROI can be drawn. The system then extracts multiple pixel columns based on the caliper settings, and edge points detected in each column are used for circle fitting. For a closed ROI, such as a circle, the calipers detect edges outward from the inside of the ROI. The caliper direction generally does not need adjustment, and rotating the ROI does not change the detection direction.
Edge Polarity	This parameter specifies the direction in which the grayscale values change at the edges. Value list: Dark to light: Detects edges where grayscale values increase from low to high, corresponding to a visual transition from dark to bright. Light to dark: Detects edges where grayscale values decrease from high to low, corresponding to a visual transition from bright to dark. Any: No limit on the direction of grayscale value change of the edge. Both types can be detected.
Filter Window Size	Specify the window size to be used when filtering each column of pixels in its direction. Filtering can reduce noise and improve the stability of edge detection results.
Edge Type	Define the edge types to be retained in edge detection. Value list: Best, First, Last.
Gray Value Change Threshold	This parameter specifies the minimum gray value change between adjacent pixels at the edge of an extracted pixel column required for edge point detection. Setting this parameter value properly can effectively filter out weak edges and noise.
Use Relative Threshold	Once selected, an edge point is detected only if the gray value change between adjacent pixels at the edge of a pixel column meets or exceeds the specified percentage of the maximum change in that column. Once this parameter is selected, set Relative Threshold.
Outlier Fraction	The percentage of outlier points to be removed during circle fitting.

Parameter

Description

ROI Settings

A circular ROI can be drawn. The system then extracts multiple pixel columns based on the caliper settings, and edge points detected in each column are used for circle fitting.

For a closed ROI, such as a circle, the calipers detect edges outward from the inside of the ROI. The caliper direction generally does not need adjustment, and rotating the ROI does not change the detection direction.

Edge Polarity

This parameter specifies the direction in which the grayscale values change at the edges.

Value list:

Dark to light: Detects edges where grayscale values increase from low to high, corresponding to a visual transition from dark to bright.
Light to dark: Detects edges where grayscale values decrease from high to low, corresponding to a visual transition from bright to dark.
Any: No limit on the direction of grayscale value change of the edge. Both types can be detected.

Filter Window Size

Specify the window size to be used when filtering each column of pixels in its direction. Filtering can reduce noise and improve the stability of edge detection results.

Edge Type

Define the edge types to be retained in edge detection.

Value list: Best, First, Last.

Gray Value Change Threshold

This parameter specifies the minimum gray value change between adjacent pixels at the edge of an extracted pixel column required for edge point detection. Setting this parameter value properly can effectively filter out weak edges and noise.

Use Relative Threshold

Once selected, an edge point is detected only if the gray value change between adjacent pixels at the edge of a pixel column meets or exceeds the specified percentage of the maximum change in that column. Once this parameter is selected, set Relative Threshold.

Outlier Fraction

The percentage of outlier points to be removed during circle fitting.

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Detect and Fit Circle

Description

Usage Scenario

Basic Concepts

Input and Output

Input

Output

Parameter Description

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